Racefan
Well-Known Member
What is pH?
pH is one of the most common analyses in soil and water testing. An indication of the sample’s acidity, pH is actually a measurement of the activity of hydrogen ions in the sample.
pH measurements run on a scale from 0-14, with 7.0 considered neutral. Those solutions with a pH below 7.0 are considered acids, and those above 7.0 are designated bases. The pH scale is logarithmic, so a one unit change in pH actually reflects a ten-fold change in the acidity. For instance, orange juice (pH 4) is ten times more acidic than cottage cheese, which has a pH of 5.
Many industries rely heavily on pH for their processes to work properly, or to maintain expensive equipment. Breweries maintain the pH between 4.2 and 4.6 to keep infectious bacteria from breeding during the fermentation process. In many industrial applications, if the pH is too low the water may corrode metal equipment, but if it is too high scaling may result.
pH can be measured visually or electronically. Visual comparisons use a pH indicator whose color change reflects the pH, which is then matched to a color
standard. pH meters, such as the pH 5, simplify the pH test. A probe is placed in
the sample, and the pH is read directly from the meter.
While the meter is very easy to use, the electronics within the meter are more
complex. After the pH probe measures the millivolts of potential between the
reference electrode and the pH electrode, the meter converts this reading to pH
units using the Nernst Equation:
where Ex = constant depending upon reference electrode
R= constant
Tk = absolute temperature
n = charge of the ion (including sign)
F = constant
ai = activity of the ion
Electrode Cleaning
Because your pH electrode is susceptible to dirt and contamination, clean it
every one to three months depending on extent and condition of use.
Clean the electrode in a mild detergent solution. Wipe the probe with a soft
tissue paper. Avoid touching the glass membrane with your fingers. Rinse
thoroughly in tap water and then in distilled water. Recalibrate your meter after
cleaning the electrode.
Storage
The pH electrode should always be stored in the soaker bottle. The cap should
be tightened to prevent leaks. The soaker bottle contains a dilute solution of
potassium chloride.
Special Cleaning Tips
Salt deposit: dissolve the deposit by immersing the electrode in tap water for ten
to fifteen minutes. Then thoroughly rinse with distilled water.
Oil/grease film: wash electrode pH bulb gently in detergent solution. Rinse
electrode tip with distilled water.
Clogged reference junction: heat a diluted KC1 solution to 60-80°C. Place the
sensing part of the electrode into the heated solution for about 10 minutes.
Allow the electrode to cool in some unheated KC1 solution.
Protein deposits: prepare a 1% pepsin solution in 0.1M of HC1. Place the
electrode in the solution for five to ten minutes. Rinse the electrode with
distilled water.
pH is one of the most common analyses in soil and water testing. An indication of the sample’s acidity, pH is actually a measurement of the activity of hydrogen ions in the sample.
pH measurements run on a scale from 0-14, with 7.0 considered neutral. Those solutions with a pH below 7.0 are considered acids, and those above 7.0 are designated bases. The pH scale is logarithmic, so a one unit change in pH actually reflects a ten-fold change in the acidity. For instance, orange juice (pH 4) is ten times more acidic than cottage cheese, which has a pH of 5.
Many industries rely heavily on pH for their processes to work properly, or to maintain expensive equipment. Breweries maintain the pH between 4.2 and 4.6 to keep infectious bacteria from breeding during the fermentation process. In many industrial applications, if the pH is too low the water may corrode metal equipment, but if it is too high scaling may result.
pH can be measured visually or electronically. Visual comparisons use a pH indicator whose color change reflects the pH, which is then matched to a color
standard. pH meters, such as the pH 5, simplify the pH test. A probe is placed in
the sample, and the pH is read directly from the meter.
While the meter is very easy to use, the electronics within the meter are more
complex. After the pH probe measures the millivolts of potential between the
reference electrode and the pH electrode, the meter converts this reading to pH
units using the Nernst Equation:
where Ex = constant depending upon reference electrode
R= constant
Tk = absolute temperature
n = charge of the ion (including sign)
F = constant
ai = activity of the ion
Electrode Cleaning
Because your pH electrode is susceptible to dirt and contamination, clean it
every one to three months depending on extent and condition of use.
Clean the electrode in a mild detergent solution. Wipe the probe with a soft
tissue paper. Avoid touching the glass membrane with your fingers. Rinse
thoroughly in tap water and then in distilled water. Recalibrate your meter after
cleaning the electrode.
Storage
The pH electrode should always be stored in the soaker bottle. The cap should
be tightened to prevent leaks. The soaker bottle contains a dilute solution of
potassium chloride.
Special Cleaning Tips
Salt deposit: dissolve the deposit by immersing the electrode in tap water for ten
to fifteen minutes. Then thoroughly rinse with distilled water.
Oil/grease film: wash electrode pH bulb gently in detergent solution. Rinse
electrode tip with distilled water.
Clogged reference junction: heat a diluted KC1 solution to 60-80°C. Place the
sensing part of the electrode into the heated solution for about 10 minutes.
Allow the electrode to cool in some unheated KC1 solution.
Protein deposits: prepare a 1% pepsin solution in 0.1M of HC1. Place the
electrode in the solution for five to ten minutes. Rinse the electrode with
distilled water.
